Ferrate(VI), or “ferrate”, has long been known as a powerful oxidant that has found uses in waste water treatment and in batteries. The literature also contains reports of the use of ferrate in certain organic oxidations, surface treatments, and blood clotting.
There are several ways of synthesizing ferrate. One such method is described by Johnson in U.S. Pat. No. 5,746,994 in which Fe3+ is oxidized with monoperoxide. Johnson reports that the isolation of potassium ferrate(VI) K2FeO4 in a sulfate matrix K2SO4 stabilizes the ferrate against decomposition and inhibits clumping from moisture adsorption. Johnson also mentions that potassium ferrate made by hypochlorite oxidation in strongly alkaline solution and precipitated by the addition of KOH is stable indefinitely when kept dry.
An apparatus for synthesizing ferrate is described in U.S. Published Patent Application No. 2005/0042155 A1.
Ferrate has been proposed for use commercially for water purification and its use in treating waste water has been discussed in scores of publications. For example, Deininger et al. in U.S. Pat. Nos. 4,983,306 and 5,380,443 has described treating water to remove metal ion contaminants, especially the transuranic elements. In this method, the pH of the water is adjusted to about 6.5 to about 14. Ferrate is especially useful for waste water treatment since it can remove a broad range of contaminants, disinfects many types of pathogens, and the iron(III) products coagulate and fall from solution, thereby also clarifying the water.
The use of ferrate in the presence of a phase transfer catalyst has been reported in oxidations of certain organic compounds. Song et al., in Huaxue Tongbao 69(3), 220-223 (2006) reported the conversion of benzyl alcohol to benzaldehyde by reaction with potassium ferrate in the cyclohexane/water in the presence of benzyltrimethylammonium chloride. Similar chemistry was described by Kim et al. in Synthesis, 10, 866-8 (1984).
Patterson in U.S. Pat. No. 6,521,265 described a method of clotting blood by topically applying a ferrate paste to a wound. In this method, the compound is stored dry and unmixed and is mixed into a paste with the patient's blood or other aqueous media just prior to its application to a wound. Patterson states that the oxygen produced during the reaction substantially reduces the level of bacteria, virus and fungus at the wound. After treatment, the wound remains open unless the ferrate salt is combined with a bandage that has been impregnated or coated with a dry powder of one of the ferrate salt compositions.
Metal surfaces can be oxidized with a ferrate solution to form an oxide layer. Minevski et al. in U.S. Pat. No. 7,045,024 describe a process in which an aluminum surface is cleaned and then treated with a ferrate solution for a time ranging from about 1 second to about 5 minutes.
Champi et al. in U.S. Pat. No. 6,974,562 and U.S. Published Patent Application No. 2005/0271575 A1 describe methods of making ferrate immediately prior to use. This is advantageous since ferrate can degrade quickly in the presence of moisture. Champi et al. suggest that the ferrate could be encapsulated for future use in a membrane of molecular sieves, clay, porcelain, or other porous material that is not susceptible to oxidation. The membrane could be slightly water soluble so that the ferrate could be released over time. Champi et al. propose numerous uses for the ferrate, including: as an oxidant to prepare polymer and metal surfaces; removal of color from industrial electrolytic baths, synthesis of Fischer-Tropsch catalysts, purifying hemicellulose, as a selective oxidant in organic chemistry, disinfection as a biocide or virocide, phosphorylase inactivator, paint additive, denitration of flue gas, electrode, detoxifying cyanide from waste water, in cigarette filters, as an oxidant of pulp waste, removal of hydrogen sulfide, purifying waste water and drinking water, as an additive to cement as a structural hardener; as a disinfectant, removal of slime films such as in power plants and shipboard cooling systems, delignification of agricultural residues, magnetic filler for plastics, as a catalyst in burning coal, as a component of grinding wheels, in ceramic encapsulated rare earth ferrates where ferromagnetic properties are needed, removal of textile dyes from wastewater, treatment of boiler chemical cleaning wastes, oxidizing sulfur and cyanide containing compounds generated by oil refineries and coke processing plants, removing Mn from drinking water, removing As from drinking water, destroying chemical warfare agents, removing organic matter from drinking water, purifying water in a Jacuzzi or swimming pool and filtering away the resulting iron salts, cleaning waste water from animal and vegetable processing, treatment of any aqueous stream containing biosolids, radioactive cleanup, oxidizing pretreatment of chromium containing films, removing heavy metals from solution, cleaning or disinfecting metallic surfaces in medical devices or in the semi-conductor industry, disinfecting and cleaning instruments and surfaces for medical uses, and cleaning bilge water from ships.